Subcellular biochemical studies of a naturally occurring enteropathy in the dog resembling chronic tropical sprue in human beings.

Subcellular biochemical features of a naturally occurring enteropathy in the dog resembling chronic tropical sprue in human beings were examined. Affected dogs had reduced xylose absorption and low concentrations of serum folate, RBC folate, and serum vitamin B12. Histologic examination of peroral jejunal biopsy specimens revealed villous atrophy and a variable infiltration of lymphocytes and plasma cells in the lamina propria. Biochemical assessment of the principal subcellular organelles was achieved by the assay of specific marker enzymes in homogenized jejunal biopsy specimens and in the gradient fractions after isopyknic centrifugation on continuous sucrose-density gradients. Activities of brush-border marker enzymes were reduced. However, there was no change in the equilibrium density of this organelle, indicating that these quantitative brush-border changes were not accompanied by an alteration in the composition of the microvillous membrane. Activities of lysosomal enzymes were increased, and there was evidence of enhanced lysosomal fragility and a proliferation of the endoplasmic reticulum. These findings were consistent with an impairment of the functional capacity of the small intestinal mucosa and implicated lysosomes and the endoplasmic reticulum in the disease process.